Differences between primary and permanent teeth

DIFFERENCES BETWEEN
PRIMARY AND PERMANENT
TEETH
Presented by-
Dr. Mathew Thomas Maliael
BDS

CONTENTS
 Introduction
 General differences
 Eruption sequences
 Crown
 Pulp
 Root
 Enamel
 Dentin
 Periodontium
 Histological differences
 Individual differences in morphology of tooth

INTRODUCTION
 Primary teeth are also called as temporary , milk ,
deciduous or baby teeth.
 They are present from infancy stage till early
teenage.
 Though they are erroneously considered as a
annoyance , they play a major role in mastication
and maintaining space for eruption of permanent
teeth.
 Significant differences in different aspects
distinguish them from their permanent counterparts.

GENERAL DIFFERENCES
 No. of teeth present:- primary-20
permanent – 28-32
 Teeth formula:- ICPM/ICPM
primary- 2102/2102
permanent- 2123/2123
 Bicuspids and third molars are absent in the primary set of
tooth.
 Primary teeth are smaller in size when compare to permanent
teeth.
 1st tooth to erupt into the oral cavity is mandibular incisor
whereas in permanent teeth it is the mandibular first molar.
 Primate space is absent in primary teeth.
 Primary teeth are present within the age of 6 months-10 to 12
years ( @ the age of 13 years only about 5% of primary teeth
remains).

 Eruption sequence follows a pattern –
incisors-first molars- canines-second molars.
 This pattern is generally followed by both arches,
with the mandibular arch preceding the maxillary
arch.
 The loss of deciduous teeth tends to mirror the
eruption sequence.
 Caries susceptibility is reverse of this order.

CROWN
 Bluish white in color. Refractive
index similar to that of milk(
RI=1).
 smaller in all dimensions .
Exposed area is about one-half
that of the permanent teeth.
 Wider mesio-distally in relation
to cervico-occlusal dimension.
this gives a cup shaped
appearance to the anterior
teeth and squat shaped
appearance to the molars.
 Grayish white to yellowish
white in color.
 Larger in dimensions.
 Larger in cervico-occlusal
dimension than the mesio-
distal dimension. this gives a
longer appearance to
permanent anterior teeth.
PRIMARY TEETH PERMANENT TEETH

 Cuspids are slender and to be
more conical.
 Cervical ridges are more
pronounced especially on
buccal aspect of first primary
molar.
 Buccal and lingual surface of
molars , especially 1st molar,
converge towards occlusal
surface so they have a narrow
occlusal table in the bucco-
lingual plane.
 Cuspids are less conical.
 The cervical ridges are flatter.
 There is less convergence of
buccal and lingual surface of
molars towards occlusal
surface.

 Occlusal plane is relatively flat.
 Molars are bulbous and are
sharply constricted cervically.
 The contact areas between
molars are broader , flatter and
situated gingivally.
 Occlusal plane has relatively
curved contour.
 They have less constriction at
the neck.
 The contact point between
permanent molars is situated
occlusally.

 Supplemental grooves are
more.
 Mammelons are absent.
 1st molar is smaller in
dimension than the 2nd molar
 Supplemental grooves are
less.
 Mammelons are present on
incisal edges of newly erupted
incisors.
 1st molar is larger in dimension
than the 2nd molar.

PULP
(PULP CHAMBER ANATOMY IN BOTH PRIMARY AND PERMANENT TEETH CLOSELY APPROXIMATES THE
SURFACE SHAPE OF THE CROWN)
 Pulp chamber is larger in
relation to crown size.
 Pulpal outline follows DEJ
more closely.
 Pulp horns are closer to the
outer surface. Mesial pulp horn
extends to a closer
approximation of surface than
the distal pulp horn.
 High degree of cellularity and
vascularity in tissue.
 High potential for repair.
 Pulp chamber is smaller in
relation to crown size.
 Pulpal outline follows DEJ less
closely.
 The pulp horns are
comparatively away from the
outer surface.
 Comparatively less degree of
cellularity and vascularity in
tissue.
 Comparatively less potential for
repair.

 Comparatively less tooth
structure.
 Greater thickness of dentin
over occlusal fossa of molars.
 Root canals are more ribbon
like. the radicular pulp follows
a thin , tortuous and branching
path.
 Floor of pulp chamber is
porous. Accessory canals in
primary pulp chamber floor
leads directly into inter-
radicular furcation.
 More tooth structure protecting
the pulp.
 Comparatively lesser thickness
of dentin over the pulpal wall at
the occlusal fossa of molars.
 Root canals are well defined
with less branching.
 Floor of pulp chamber does not
have any accessory canal.

ROOT
 Roots are larger and more slender
in comparison to crown size.
 Furcation is more towards cervical
area so that root trunk is smaller .
 Roots are narrower mesio-distally.
 At the cervical region, the roots of
the primary molars flare outward
and continue to flare as they
approach the apices to
accommodate permanent tooth
buds.
 Undergo physiologic resorption
during shedding of primary teeth.
 Roots are shorter and bulbous
in comparison to crown.
 Placement of furcation is apical
, thus the root trunk is larger.
 Roots are broader mesio-
distally.
 Marked flaring of roots is
absent.
 Physiologic resorption is
absent.

ENAMEL
 Bands of retzius are less
common. This maybe partly
responsible for the bluish white
color.
 Neonatal lines are present in
all teeth.
 Enamel is thinner and has a
more consistent depth of about
1mm thickness throughout the
entire crown
 Enamel rods at the cervical
slopes occlusally from the DEJ.
 Bands of retzius are more
common.
 Neonatal lines are only present
in 1st molars
 The enamel is thicker and has
a thickness of about 2-3mm.
 Enamel rods are oriented
gingivally.

DENTIN
 Dentinal tubules are less
regular.
 Dentin thickness is half that of
permanent teeth. Thickness is
limited in some places.
 Less dense and easy to cut.
 Interglobular dentin is absent.
 Dentinal tubules are more
regular.
 Den.
 Dentin is thicker.
 Dentin is denser and difficult to
cut.
 Interglobular dentin is present.

PERIODONTIUM
 Cementum is very thin and o
the primary type. Secondary
cementum is characteristically
absent.
 Alveolar atrophy is rare.
 Gingivitis is generally absent in
a healthy child. Similarly
recession is in frequent.
 Secondary cementum is
present.
 Alveolar atrophy occurs.
 Gingivitis is common in adults.

HISTOLOGICAL DIFFERENCES
 Roots have enlarged apical
foramens. Thus , the abundant
blood supply demonstrates a
more typical inflammatory
response.
 Incidence of reparative dentin
formation beneath carious
lesion is more extensive and
irregular.
 Pulp nerve fibers pass to the
odontoblastic area, where they
terminate as free nerve
endings.
 Foramens are restricted. Thus
reduced blood supply favors a
calcific response and healing
by calcific scarring.
 Reparative dentin formation is
less.
 Pulp nerve fibres terminate
mainly among the odontoblasts
and even beyond the
predentin.

 Density of innervations is less
because of which primary teeth
are less susceptible to
operative procedures. Neural
tissue is the first to degenerate
when root resorption takes
place.
 Localization of infection and
inflammation is poorer in pulp
 Density of innervations is more.
 Infection and inflammation in
pulp is localized .

INDIVIDUAL DIFFERENCES IN TOOTH
MORPHOLOGY

MAXILLARY CENTRAL INCISOR
 Mesio-distal measurement is
greater than cervico-incisal
measurement.
 Labial surface is slightly
convex with little evidence
of developmental grooves.
 The incisal edge joins the
mesial surface at an acute angle
and the distal surface at a more
obtuse angle.

MAXILLARY LATERAL INCISOR
 Smaller in most
dimensions.
 Disto-incisal angle is
more rounded.
 Lingual anatomy is less
prominent.
 Root is longer in
proportion to the
crown.

MAXILLARY CANINE
 Larger than incisors in all
dimensions.
 All crown surfaces the
are convex creating a
more pronounced
constriction at the cervix
prominent cusp.
 Lingual surface presents
a lingual ridge , fossa and
marginal ridges.
 The root is long and
tapered toward the apex,
and shows increase in
diameter just apical to the
cervical line.

MANDIBULAR CENTRAL INCISOR
 Smaller in all dimensions
than MCI.
 Labially appears
symmetric, less convex
and smooth without
evidence of
developmental grooves.
 Lingual surface is usually
smooth with poorly
defined fossa and
marginal ridges.
 Root is long and evenly
tapered toward the apex.

MANDIBULAR LATERAL INCISORS
 Similar in morphology to that
of CI, except that the incisal
edge slopes downward
distallly forming a more
obtuse disto-incisal angle.
 Slightly larger cervico-
incisally and mesiodistally
than CI.
 Root is conical, longer than
that of CI and shows definite
inclination at the apex.
 Distal surface of the root will
show a longitudinal
depression or groove
separating labial and lingual
surfaces.

MANDIBULAR CANINE
 Appears more slender
than MC because of
smaller mesio-distal
diameter in relation to
crown height
 The disto-incisal edge is
longer.
 Marginal ridges and
cingulum are less
prominent.
 Labio-lingual diameter is
smaller than MC.
 Root is smoothly tapered
from the cervical line to
the apex.

MAXILLARY FIRST MOLAR
 Appears triangular when viewed
occlusally.
 Proximal surfaces converge lingually
creating a crown that is wider mesio-
distally at the bucal surface.
 Mesio-lingual cusp is the largest
followed by mesio-buccal and disto-
buccal.
 Mesially , prominent bucco-cervical
ridge can be seen
 3 long and slender roots are present.
 Lingual root is the longest
 All three roots extend from a short root
base in a divergent manner.

MAXILLARY SECOND MOLAR
 Similar to maxillary 1st permanent
premolar (crown form, pit , groove and
cusp arrangement.
 Four cusps.
 Largest is mesiolingual . Distobuccal is
the smallest and other 2 are almost of the
same size.
 Occlusal surface 3 pits which meet at the
intersection of the developmental groove
 3 roots. Lingual root is the largest and
distobuccal is the smallest.
 Root morphology is similar to that of to
that of 1st permanent molar except that
roots are flared and diverge more from
the root base.

MANDIBULAR 1ST MOLAR
 When viewed from occlusal aspect the
outline is rhomboidal in shape.
 2 buccal cusps and 1 lingual cusp.
 3 pits are found on occlusal surface of
which the surface-central is most
prominent.
 A distinguishing feature is heavy
transverse ridge connecting the mesio-
buccal and mesio-lingual cusps.
 2 roots ; mesial and distal. They show
typical flaring and end in a sharp edge
which may be slightly bifid
 The most unique feature of this tooth is
that is does not resemble any tooth in
the permanent set.

MANDIBULAR 2ND MOLAR
 Smaller replica of the mandibular 1st
permanent molar.
 3 buccal cusps;
distobuccal(largest),followed by the
mesio-buccal and the distal.
 2 lingual cups which are similar in size.
 3 pits ; central(prominent) ,mesial, distal.
 Crown morphology shows typical
cervical constriction and bucco-cervical
ridge as seen of other primary molars.
 2 roots ;mesial and distal. Narrow
mesiodistally and broad buccolingually.
 Roots are more diverged than 1st molar

MORPHOLOGIC CONSIDERATIONS
 Crowns are smaller and more bulbous than their permanent counterparts, and
the molars are bell shaped , with a definite constriction in the cervical region
 The characteristic sharp lingual inclination occlusally of the facial surfaces results
in the formation of distinct faciogingival that ends abruptly at the CEJ.
 The sharp constriction at the neck of the primary molar necessitates special care
in the formation of the gingival floor during class2 tooth preparation .
 The buccal and lingual surfaces of the molars converging sharply occlusally
results in a narrow occlusal surface or food table.
 The pulpal outline follows the DEJ more closely than that of the permanent teeth
.
 The pulpal horns are longer and more pointed than the cusps would indicate.
 The dentin also has less bulk or thickness, and so the pulp is proportionately
larger than that of the permanent teeth .
 The enamel of primary teeth is thin but of uniform thickness . The enamel surface
tends to be parallel to the DEJ.

REFERENCES
 Textbook of Pedodontics- Shoba Tandon
 Textbook of Pediatric Dentistry-Nikhil Marwah
 Dentistry for child and adolescent-McDonald &
Avery

Differences between primary and permanent teeth

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